Method for reducing pattern dimension in photoresist layer

ABSTRACT

The invention discloses improvements in the so-called coated thermal flow process for reducing the pattern dimension of a patterned resist layer on a substrate to accomplish increased fineness of resist patterning, in which a coating layer of a water-soluble resin formed on the patterned resist layer is heat-treated to effect thermal shrinkage of the coating layer with simultaneous reduction of the pattern dimension followed by removal of the coating layer by washing with water. The improvement of the process is obtained by using an aqueous coating solution admixed with a water-soluble amine compound such as triethanolamine in addition to a water-soluble resin such as a polyacrylic acid-based polymer. Further improvements can be obtained by selecting the water-soluble resin from specific copolymers including copolymers of (meth)acrylic acid and a nitrogen-containing monomer such as N-vinylpyrrolidone, N-vinylimidazolidinone and N-acryl-oylmorpholine as well as copolymers of N-vinylpyrrolidone and N-vinylimidazolidinone in a specified copolymerization ratio.

This is a continuation of Ser. No. 10/173,880, filed Jun. 19, 2002, nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in a method for obtaininga patterned photoresist layer of which the resist pattern has a reduceddimension by a post-patterning heat treatment. More particularly, theinvention relates to improvements in the method for reducing the patterndimension in a photolithographically patterned resist layer by apost-patterning procedure in which a patterned resist layer on asubstrate is provided thereon with a coating layer of a water-solubleresin and then the thus coated patterned resist layer is subjected to aheat treatment to effect thermal shrinkage of the resist layer resultingin a reduced pattern dimension followed by complete removal of thecoating layer of the water-soluble resin by washing with water.

Along with the recent trend in the technology of semiconductor devicestoward higher and higher degrees of integration and more and morecompact sizes of the devices, the photolithographic patterningtechnology of photoresist layers is also required to accomplish finerand finer patterning of the photoresist layer.

An approach for accomplishing the above mentioned requirement in thephotolithographic technology for a pattern dimension of 0.20 μm or fineris to use a patterning exposure light of very short wavelengths such asKrF excimer laser beams, ArF excimer laser beams and F₂ excimer laserbeams as well as electron beams. This approach, however, cannot besuccessful without development of a photoresist composition havingadaptability to these short-wavelength exposure radiations.

In this regard, so-called chemical-amplification photoresistcompositions are widely employed in the modern photolithographictechnology, in which the catalytic activity of an acid generated in thelight-exposed areas from a radiation-sensitive acid-generating agentcontained in the resist layer is utilized to effect a solubility changeof the resinous ingredient to give high sensitivity and patternresolution even with a small amount of the acid-generating agent.

As a method for obtaining very finely patterned resist layer on asubstrate, there is a known method in which a photoresist layer formedon a substrate is patterned in a conventional way including patterninglight-exposure and development and the thus patterned resist layer isprovided with a coating layer of a resin by utilizing the activity ofthe acid diffused from the resist layer followed by a heat treatment soas to effect reduction of the pattern dimension to be finer than theresolution limit inherent in the photoresist composition (JapanesePatent Kokai 5-166717 and 5-241348).

This method, however, has a problem in respect of the relatively largetemperature dependency amounting to more than 10 nm/° C. within thesubstrate surface. This disadvantage can hardly be overcome with theheating device currently employed in the manufacture of semiconductordevices due to poor uniformity of the temperature distribution.Accordingly, the above-described method of post-patterningdimension-reducing method cannot be practiced without substantialvariations in the pattern dimensions.

It is also known that the dimension of a patterned resist layer can bereduced below the resolution limit of the photoresist composition bysubjecting the patterned resist layer to a heat treatment or a radiationirradiation treatment to cause mobilization of the patterned resistlayer. Though advantageous in respect of small temperature dependency ofonly a few nm/° C. within the plane of the substrate surface, thismethod has a problem that, due to the difficulty in controllingmobilization of the photoresist layer by the heat treatment, uniformreduction of the dimension of the photoresist layer can hardly beexpected within the substrate surface.

Besides the above described photolithographic patterning process byutilizing excimer laser beams for patterning light exposure, proposalsare made in Japanese Patent No. 2723260 for reduction of the patterndimension, according to which a layer of an electron beam resistcomposition comprising a polymethyl methacrylate resin is patterned togive a patterned resist layer which is then provided thereon with acoating layer of a positive-working resist composition followed by aheat treatment to form a reacted layer at the interface between thepatterned resist layer and the positive-working resist layer and removalof the positive-working resist layer from the unreacted areas. JapanesePatent Kokai 6-250379 further discloses a method in which a reactedlayer is formed between the underlying patterned resist layer and theupper resist layer by utilizing the acid generated from theacid-generating agent or thermal crosslinking by the acid. JapanesePatent Kokai 10-73927 discloses a method for the manufacture ofsemiconductor devices by effecting reduction of the pattern dimension inwhich the overcoating layer is formed by using, as the coating solution,a composition prepared by dissolving a water-soluble resin,water-soluble crosslinking agent or combination thereof in awater-miscible solvent without addition of any photosensitiveingredients. Japanese Patent Kokai 2000-347414 proposes a method inwhich a substrate surface is provided thereon with a photosensitivelayer of a chemical-amplification photoresist composition which issubjected to patterning light-exposure and development to form apatterned resist layer, a coating film is formed on the patterned resistlayer by using a coating composition containing a water-soluble resinsuch as a polyvinyl acetal, water-soluble crosslinking agent such astetra(hydroxymethyl)glycoluril, a water-soluble nitrogen-containingcompound such as amines and, optionally, a fluorine- andsilicon-containing surface active agent followed by a heat treatment toform a water-insoluble reacted layer at the interface between thepatterned resist layer and the overcoating layer and finally theovercoating layer in the unreacted areas is removed by using a solvent.

Although each of the above-described methods is desirable becausereduction of the pattern dimension can be conveniently accomplished toexceed the wavelength limitation of the photoresist composition byforming an upper coating layer on the underlying photoresist layer,several disadvantages are involved therein. For example, thecrosslinking reaction of the overcoating composition may overly proceedto unnecessary portions such as the bottom of the patterned resist layerresulting in an undesirable non-orthogonal cross sectional profilethereof eventually with trailing skirts. The dimension of the upperresist layer depends on the mixing baking which is a heat treatment tocause crosslinking. Further, the temperature dependency obtained bythese methods is relatively large to be 10 nm/° C. or larger so that itis very difficult to ensure high uniformity of the pattern dimensionwithin the substrate surface when the substrate has a large size or thepatterned resist layer is extremely fine resulting in poorcontrollability in reduction of the pattern dimension.

Besides, a proposal is made in Japanese Patent Kokai 1-307228 and4-364021 for the so-called thermal flow process in which a patternedphotoresist layer formed on a substrate is subjected to a heat treatmentor radiation-irradiation treatment to effect mobilization of the resistlayer so as to accomplish reduction of the pattern dimension to becomefiner than the resolution limit of the photoresist composition.

This method, however, is defective because products of reproduciblequality can hardly be obtained due to the difficulty encountered incontrolling the mobility of the resist by means of heat or radiation. Asa further development of this thermal flow process, Japanese PatentKokai 7-45510 proposes a method in which the mobility of the resist iscontrolled by providing a coating layer of a water-soluble resin on thepatterned photoresist layer formed on a substrate. Since thewater-soluble resin used in this method, such as polyvinyl alcohols, isinsufficient in the solubility in water required in the removal withwater and long-term stability, troubles are sometimes caused by theresidual resin film remaining unremoved with water.

SUMMARY OF THE INVENTION

In view of the above described problems and disadvantages in the priorart, the present invention has an object to provide an improvement inthe method for reducing the dimension of a patterned photoresist layerby a post-patterning treatment in which the patterned resist layer isprovided thereon with a coating layer of a water-soluble resincomposition followed by a heat treatment to cause reduction of thepattern dimension or the distance between the resist patterns and thenremoval of the water-soluble coating layer away from the patternedresist layer by washing with water.

Thus, in a first aspect of the invention, the present inventionprovides, in a method for reducing a pattern dimension in a patternedphotoresist layer formed on a substrate by a post-patterning heattreatment, referred to as the coated thermal flow process hereinafter,comprising the steps of: (a) forming a coating layer of a water-solubleresin composition on the patterned resist layer, (b) drying the coatinglayer of the aqueous coating solution, (c) subjecting the dried coatinglayer and the patterned resist layer to a heat treatment to effectthermal shrinkage of the patterned resist layer with reduction of thepattern dimension and (d) removing the coating layer of thewater-soluble resin composition, the improvement which comprises: using,in step (a), a coating solution containing a water-soluble resin and awater-soluble amine compound having, preferably, a pKa value of 7.5 to13.0 at 25° C. for the formation of the coating layer.

In a second aspect of the invention, the improvement provided by thepresent invention comprises, in step (a) of the coated thermal flowprocess, using an aqueous coating solution containing a water-solubleresin which is a copolymer of (A) acrylic acid, methacrylic acid or acombination thereof and (B) a water-soluble ethylenically unsaturatedcompound which is exemplified by N-vinylpyrrolidone,N-vinylimidazolidinone, methyl acrylate, methyl methacrylate,N,N-dimethylacrylamide, N,N-dimethylaminopropyl methacrylamide,N,N-dimethylaminopropyl acrylamide, N-methhylacrylamide,diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate,N-acryloylmorpholine and the like, of which those nitrogen-containingwater-soluble compounds are preferable, or a combination thereof.

In a third aspect of the invention, the present invention is directed toan improvement of the aqueous coating solution for use in step (a) ofthe coated thermal flow process in which the water-soluble resin is acopolymer of N-vinylpyrrolidone and a water-soluble monomeric vinylcompound other than N-vinylpyrrolidone which is preferablyN-vinylimidazolidinone.

In a fourth aspect of the invention, the present invention provides, inthe above-mentioned coated thermal flow process of a patterned resistlayer, the improvement which comprises, as a guideline for the selectionof the water-soluble resin in step (a) of the method using an aqueouscoating solution containing a water-soluble resin exhibiting such awater-solubility behavior that, in a testing procedure comprising thesteps of forming a coating layer of the resin on an unpatternedphotocured layer of the photoresist composition, subjecting the coatinglayer to a heat treatment at 140° C. for 60 seconds and removing awaythe coating film by washing with water at 23° C., the coating layer canbe completely removed within 60 seconds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides, according to the first aspect of theinvention, an improvement in the formulation of the aqueous coatingsolution used for the formation of a water-soluble coating layer on apatterned photoresist layer in step (a) of the so-called coated thermalflow process, in which the coating layer and the patterned resist layerare subjected to a heat treatment, for example, at 80 to 160° C. for 30to 90 seconds followed by complete removal of the coating layer bywashing with water. The temperature of this heat treatment shouldpreferably be lower than the softening point of the patterned resistlayer. When the heat treatment is conducted at such a temperature, thepatterned resist layer receives a tension from the coating layer to givemore remarkable reduction in the dimension of holes and trenches with adecrease in the dependency on the duty ratio, i.e. the line distancewithin the plane of substrate surface. The above-mentioned softeningpoint of the resist layer is a temperature at which, when the patternedresist layer formed on a substrate is gradually heated, an incipientspontaneous flow of the mobilized resist layer is detected.

The water-soluble resin contained in the aqueous coating solution usedin the coated thermal flow process is not particularly limitative andcan be selected from a variety of water-soluble polymers includingalkyleneglycol-based polymers, cellulosic polymers, vinyl polymers,acrylic polymers, urea-based polymers, epoxy polymers, melamine-basedpolymers and polyamide polymers. Although any of these water-solublepolymers can be used either singly or as a combination of two kinds ormore, it is preferable in respect of the efficiency for reduction of thepattern distance without affecting the cross sectional profile of thepatterned resist layer that the water-soluble resin is a homopolymer ofan acrylic monomer or a copolymer of an acrylic monomer with othercopolymerizable monomers.

Examples of the above-mentioned acrylic monomer include acrylic acid,methyl acrylate, methacrylic acid, methyl methacrylate, N,N-dimethylacrylamide, N,N-dimethylaminopropyl methacrylamide,N,N-dimethylaminopropyl acrylamide, N-methyl acrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate and N-acryloylmorpholine.

Examples of the comonomer compound copolymerized with the above namedacrylic monomers include vinyl monomers such as N-vinylpyrrolidone,N-vinylimidazolidinone, vinyl acetate and the like.

The aqueous coating solution used in step (a) of the coated thermal flowprocess is prepared by dissolving one or a combination of the abovenamed water-soluble resins in water in a concentration of 3 to 50% byweight or, preferably, 5 to 20% by weight. When the concentration is toolow, the coating layer formed from the coating solution is sometimesincomplete while, when the concentration is too high, the desired effectof the coated thermal flow process can little be accomplished.

According to the first aspect of the invention, the aqueous coatingsolution as described above is further admixed with a water-solubleamine compound which, preferably, has a pKa value of 7.5 to 13.0 at 25°C. Examples of suitable amine compounds include alkanolamines such asmonoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylehtanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine, triisopropanolamine and thelike, polyalkylene polyamines such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N′-diethylethylenediamine,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine, 1,6-hexanediamine and the like, aliphatic aminessuch as 2-ethylhexylamine, dioctylamine, tributylamine, tripropylamine,triallylamine, heptylamine, cyclohexylamine and the like, aromaticamines such as benzylamine, diphenylamine and the like and cyclic aminessuch as piperazine, N-methylpiperazine, methylpiperazine,hydroxyethylpiperazine and the like. These amine compounds can be usedeither singly or as a combination of two kinds or more. It ispreferable, however, that the water-soluble amine compound has a boilingpoint of 140° C. or higher under normal pressure in order not to be lostby the heat treatment of the coating layer. In this regard,monoethanolamine and triethanolamine are suitable.

The amount of the water-soluble amine compound added to the aqueouscoating solution is in the range from 0.1 to 30% by weight or,preferably, from 2 to 15% by weight based on the amount of thewater-soluble resin. When the amount of the amine compound is too small,the aqueous coating solution eventually suffers a decrease in storagestability due to degradation. When the amount exceeds 30% by weight, inparticular, an adverse effect is caused on the cross sectional profileof the patterned resist layer. The problem of denaturation of theaqueous coating solution can be at least partly solved by admixing thecoating solution with an acidic compound such as p-toluene sulfonic acidand dodecylbenzene sulfonic acid. The coating layer can be imparted withincreased stability by admixing the aqueous coating solution with asurface active agent.

In the method according to the first aspect of the present invention,the patterned resist layer formed on a substrate is coated at leastpartly with the above described aqueous coating solution followed bydrying to give a dried coating layer and then subjected to a heattreatment which can be conducted in substantially the same manner as inthe conventional thermal flow process. Namely, the patterned resistlayer is coated with the coating solution of the water-soluble resin byusing a coating machine such as a spinner and the coating layer is driedby heating at about 80 to 160° C. for 30 to 90 seconds. It is optionalthat the patterned resist layer coated with the water-soluble resin issubjected beforehand to a pre-baking treatment at 80 to 100° C. for 30to 90 seconds. The concentration of the water-soluble resin in theaqueous coating solution is in the range from 3 to 50% by weight or,preferably, from 5 to 20% by weight depending on the desired thicknessof the coating layer which is in the range from 0.1 to 0.5 μm.

The aqueous solvent used in the above-described aqueous coating solutionis usually water but it is optional that the solvent is a mixture ofwater with a water-miscible alcoholic solvent such as methyl alcohol,ethyl alcohol, propyl alcohol, isopropyl alcohol, glycerin,ethyleneglycol, propyleneglycol, 1,2-butyleneglycol, 1,3-butyleneglycoland 2,3-butyleneglycol. These water-miscible alcoholic solvents can beadded to water in a mixing proportion not exceeding 30% by weight basedon water.

According to the first aspect of the invention, reduction of the resistpattern dimension accomplished by the coated thermal flow process can beto such an extent that the width of a trench pattern is decreased from220 nm to 160 nm and the diameter of a hole pattern is decreased from180 nm to 160 nm. After the thus accomplished thermal shrinkage of thepatterned resist layer, the coating layer of the water-soluble resinformed thereon is completely removed by washing for 10 to 60 secondswith an aqueous solvent which is preferably water.

A finely patterned resist layer formed by the photolithographictechnology can be imparted in this way with an increased fineness of thepattern dimension to exceed the resolution limit accomplished in aconventional process without affecting other characteristics requiredfor the finely patterned resist layer.

According to the second aspect of the invention, the present inventionprovides an aqueous coating solution for use in the coated thermal flowprocess, of which the water-soluble resin is a copolymer consisting ofthe monomeric units comprising (A) the monomeric units derived fromacrylic acid, methacrylic acid or a combination of acrylic andmethacrylic acids and (B) the monomeric units derived from various kindsof ethylenically unsaturated monomeric compounds named before including,as preferable ones, N-vinylpyrrolidone, N-vinylimidazolidinone,N-acryloylmorpholine or a combination thereof in a molar ratio of(A):(B) in the range from 4:1 to 1:1. It is preferable that the molarfraction of the monomeric units (A) is larger than that of the units(B). Though not particularly limitative, it is preferable in respect ofgood film-forming behavior that the above-mentioned binary copolymericresin has a weight-average molecular weight in the range from 10000 to50000 as measured by the gel permeation chromatographic method makingreference to polymethyl methacrylate resins having known molecularweights.

While the coating solution used in step (a) of the inventive method isbasically an aqueous solution of the aforementioned water-solublecopolymeric resin, it is optional that the aqueous solution furthercontains water-soluble resins of other types in a limited amountincluding cellulose derivatives, alkyleneglycol-based polymers,urea-based polymers and melamine-based polymers.

The cellulose derivative mentioned above is exemplified by hydroxypropylmethyl cellulose phthalate, hydroxypropyl methyl cellulose acetatephthalate, hydroxypropyl methyl cellulose hexahydrophthalate,hydroxypropyl methyl cellulose acetate succinate, hydroxypropyl methylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, celluloseacetate hexahydrophthalate, carboxylmethyl cellulose, ethyl celluloseand methyl cellulose. The alkyleneglycol-based copolymer is exemplifiedby addition-polymerized polymers and copolymers of ethyleneglycol,propyleneglycol, butyleneglycol and the like. The urea-based polymer isexemplified by the polymers of methylolated urea, dimethylolated urea,ethyleneurea and the like. The melamine-based polymer is exemplified bythe polymers of methoxymethylated melamine, methoxymethylatedisobutoxymethylated melamine, methoxyethylated melamine and the like.Besides, epoxy-based polymers and amide-based polymers can also be used,if water-soluble. These water-soluble resins can be used either singlyor as a combination of two kinds or more.

The aqueous solvent used in the above-described aqueous coating solutionis usually water but it is optional that the solvent is a mixture ofwater with a water-miscible alcoholic solvent such as methyl alcohol,ethyl alcohol, propyl alcohol, isopropyl alcohol, glycerin,ethyleneglycol, propyleneglycol, 1,2-butyleneglycol, 1,3-butyleneglycoland 2,3-butyleneglycol. These water-miscible alcoholic solvents can beadded to water in a mixing proportion not exceeding 30% by weight basedon water.

In the fine resist pattern-forming method according to the invention, adesired fine resist pattern can be obtained with good efficiency bysuccessively undertaking the steps including: step (a2) for theformation of a resist pattern on a substrate; step (b2) for theformation of a coating layer of a water-soluble resin on the resistpattern; step (c2) for a heat treatment of the coating layer and step(d2) for the removal of the coating layer by washing with water each asdescribed below.

The step (a2) is a step for the formation of a resist pattern on asubstrate by using a resist composition. In this step, which can beconducted according to a conventional photolithographic fine patterningprocedure in the manufacture of semiconductor devices, a substrate suchas a semiconductor silicon wafer is coated by spin coating with asolution of a chemical-amplification resist, electron beam resist or F₂laser beam resist to form a resist layer which is pattern-wise exposedto light through a photomask bearing a desired pattern or subjected toscanning with electron beams followed by a post-exposure bakingtreatment and then subjected to a development treatment with an aqueousalkaline solution as a developer such as a 1-10% by weight aqueoussolution of tetramethylammonium hydroxide to form the desired resistpattern.

The step (b2) is for the formation of a water-soluble resinous coatinglayer on the resist pattern wholly or partially by using theabove-described aqueous coating solution of a water-soluble resin. Thecoating method can be the same as that under conventional use in thethermal flow process by using, for example, a spinner, if necessary,followed by heating for drying. The coating layer has a thickness,preferably, in the range from 0.1 to 0.5 μm.

The step (c2) is for a heat treatment of the resist pattern coated witha water-soluble resinous layer in step (b2) so as to decrease thedistance between adjacent resist patterns. The heat treatment isconducted usually at a temperature of 80 to 160° C. for 30 to 120seconds. It is preferable that the heat treatment is conducted at atemperature lower than the softening point of the patterned resist layerbecause the shrinkage rate of the resist pattern is free from dependencyon the duty ratio and fineness of holes and trenches can be furtherincreased by the attractive force exerted by the water-soluble resinouscoating layer on the resist pattern. By this heat treatment, a decreasein the dimensions of the resist pattern can be obtained from 220 nm to160 nm for trenches and from 180 nm to 160 nm for holes.

In step (d2), the water-soluble coating layer covering the resistpattern after the heat treatment in step (c2) is removed by washing withan aqueous solvent or, preferably, deionized water. Removal of thecoating layer can be complete by washing usually for 10 to 60 seconds.

In essence, the present invention according to the second aspect of theinvention also provides an improved coated thermal flow process in whichthe aqueous coating solution for the formation of a coating layer on apatterned resist layer contains the above defined copolymeric resin asthe resinous ingredient and the heat treatment of the water-solublecoating layer is conducted at a temperature lower than the softeningtemperature of the patterned resist layer. While the above mentionedheat treatment of the coating layer is conducted usually at 80 to 160°C. for 30 to 120 seconds, it is preferable that the heat treatmenttemperature is lower than the softening point of the patterned resistlayer so that the patterned resist layer is subjected to traction by thethermally shrinking coating layer to cause efficient reduction of theresist pattern dimension with a rate of shrinkage not depending on theduty ratio.

According to the third aspect of the invention, the present inventionprovides an improved aqueous coating solution used in the coated thermalflow process, in which the water-soluble resinous ingredient containedin the aqueous coating solution is a copolymeric resin consisting of themonomeric units comprising (A1) the monomeric units derived fromN-vinylpyrrolidone and (B1) the monomeric units derived from awater-soluble monomeric vinyl compound other than N-vinylpyrrolidonewhich is preferably N-vinylimidazolidinone in a molar ratio of (A1):(B1)in the range from 1:9 to 9:1. Though not particularly limitative, it ispreferable in respect of good film-forming behavior and heat resistanceto withstand the heat treatment that the above-mentioned binarycopolymeric resin has a weight-average molecular weight in the rangefrom 10000 to 50000 as measured by the gel permeation chromatographicmethod making reference to polymethyl methacrylate resins having knownmolecular weights. The coated thermal flow process using the aqueouscoating solution containing the above-defined copolymeric resin isconducted in the same way as in the second aspect of the invention.

According to the fourth aspect of the invention, the improvementprovided by the present invention is related to a testing procedure forselection of the water-soluble resin as the solute in the aqueouscoating solution for the formation of a water-soluble coating layer on apatterned resist layer in the coated thermal flow process.

In practicing the solubility test of the water-soluble resin, a coatinglayer of the water-soluble resin is formed on an unpatterned butphotocured resist layer on a substrate and subjected to a heat treatmentat 140° C. for 60 seconds. Thereafter, the thus heat-treated coatinglayer of the water-soluble resin is washed with water at 23° C. todetermine the time taken for complete removal of the coating layer bydissolving away with water, which must be 60 seconds or shorter in orderfor the resin to be used in the coated thermal flow process according tothe present invention.

According to the above-described testing procedure for the solubilitybehavior of the water-soluble resin, a polymeric resin selected fromwater-soluble acrylic polymers, vinyl polymers, cellulose derivatives,alkyleneglycol-based polymers, urea-based polymers, melamine-basedpolymers, epoxy-based polymers and amide-based polymers which passes thetest can be used as the resinous ingredient in the aqueous coatingsolution. The solubility behavior of the water-soluble resin can beadjusted by copolymerizing the above-mentioned acrylic monomer with aminor amount of comonomers of other types.

In the following, the present invention in various aspects is describedin more detail by way of Examples and Comparative Examples, which,however, never limit the scope of the invention in any way.

In the Examples and Comparative Examples described below, thewater-soluble resins as a solute in the aqueous coating solution weresubjected to a solubility test in the following manner. Thus, asemiconductor silicon wafer was uniformly coated on a spinner with achemical-amplification positive-working photoresist solution(TDUR-P036PM, a product by Tokyo Ohka Kogyo Co.) followed by a dryingheat treatment at 80° C. for 90 seconds to give a dried resist layerhaving a thickness of 0.7 μm. The resist layer was then coated uniformlywith an aqueous solution of the resin on test and the coating layer wassubjected to a heat treatment at 140° C. for 60 seconds to give acoating layer of 0.3 μm thickness. The substrate bearing the thusheat-treated coating layer was kept in water at 23° C. under vibrationto determine the length of time taken before complete dissolution andremoval of the coating layer. As a criterion, the water-soluble resinswere taken as acceptable when this dissolving took a time not exceeding60 seconds.

EXAMPLE 1

A semiconductor silicon wafer was uniformly coated on a spinner with apositive-working photoresist composition (TDUR-P036PM, a product byTokyo Ohka Kogyo Co.) followed by a baking treatment at 80° C. for 90seconds to form a photoresist layer having a thickness of 560 nm.

The photoresist layer was subjected to a patterning light-exposuretreatment with KrF excimer laser beams on a light-exposure machine(Model Canon FPA-3000EX3, manufactured by Canon Co.) followed by apost-exposure baking treatment at 120° C. for 90 seconds and thensubjected to a development treatment with a 2.38% by weight aqueoussolution of tetramethylammonium hydroxide to give a hole pattern havinga diameter of 182.3 nm.

In the next place, the resist layer having the thus formed hole patternwas coated with a coating solution prepared by dissolving 9.1 g of acopolymeric resin of acrylic acid and N-vinylpyrrolidone in acopolymerization ratio of 2:1 by weight and 0.9 g of triethanolamine in90 g of water to form a coating layer which was subjected to a heattreatment at 120° C. for 60 seconds to cause thermal shrinkage followedby washing with water at 23° C. to dissolve away the coating layer. Theresult was that the coating layer could be completely removed by washingfor about 1 minute with a reduction of the hole pattern diameter to161.5 nm.

COMPARATIVE EXAMPLE 1

The experimental procedure was substantially the same as in Example 1except that the coating solution was a 5% by weight aqueous solution ofa polyvinyl alcohol. The result obtained by washing away of the coatingfilm with water was that visually recognizable residue of the coatinglayer was found.

EXAMPLE 2

A semiconductor silicon wafer was uniformly coated on a spinner with apositive-working photoresist composition (TDMR-AR2000, a product byTokyo Ohka Kogyo Co.) followed by a pre-baking treatment at 90° C. for90 seconds to form a photoresist layer having a thickness of 1.3 μm.

In the next place, the photoresist layer was subjected to patterninglight exposure on an i-line light-exposure machine (Model Nikon NSR-2205il4E, manufactured by Nikon Co.) followed by a post-exposure bakingtreatment at 110° C. for 90 seconds and then subjected to a developmenttreatment to give a trench pattern of 411.1 nm width.

The thus formed trench-patterned resist layer was provided in the samemanner as in Example 1 with a coating layer of the water-soluble resinfollowed by a heat treatment to effect thermal shrinkage and thenwashing away of the coating layer with water. The result was that thewidth of the trench pattern had been reduced from 411.1 nm to 219.5 nm.

EXAMPLE 3

The experimental procedure was substantially the same as in Example 1except that the coating solution of a water-soluble resin was preparedby dissolving, in 90 g of water, 9.5 g of a copolymeric resin of acrylicacid and N-vinylpyrrolidone in a copolymerization ratio of 2:1 by weightand 0.5 g of monoethanolamine. The result was that the hole patterndiameter could be reduced from 182.3 nm to 160.3 nm.

EXAMPLE 4

A semiconductor silicon wafer was uniformly coated with apositive-working photoresist composition (EP-TF004EL, a product by TokyoOhka Kogyo Co.) on a spinner followed by a pre-baking treatment at 150°C. for 300 seconds to form a resist layer having a thickness of 2.0 μm.

The thus formed resist layer was pattern-wise irradiated by scanningelectron beams on an electron-beam image tracing machine (Model HITACHIHL800D50 Kv, manufactured by Hitachi Ltd.) followed by a post-exposurebaking treatment at 140° C. for 300 seconds and then subjected to adevelopment treatment with a 2.38% by weight aqueous solution oftetramethylammonium hydroxide to give a trench-patterned resist layerhaving a trench width of 228.0 nm.

The thus trench-patterned resist layer was coated with the same aqueouscoating solution as used in Example 1 and the coating layer wassubjected to a heat treatment at 150° C. for 90 seconds to effectthermal shrinkage followed by washing away of the coating layer withwater to find that removal of the coating layer was complete afterwashing for about 60 seconds. The width of the trench pattern wasreduced from 228.0 nm to 155.0 nm.

EXAMPLE 5

A semiconductor silicon wafer was uniformly coated on a spinner with apositive-working photoresist solution (TDUR-P036PM, supra) followed by apre-baking treatment at 80° C. for 90 seconds to give a photoresistlayer of 560 nm thickness, which was pattern-wise light-exposed on alight-exposure machine (Model Canon FPA-3000EX3, supra) and, after apost-exposure baking treatment at 120° C. for 90 seconds, subjected to adevelopment treatment with a 2.38% by weight aqueous solution oftetramethylammonium hydroxide to give a patterned resist layer having ahole pattern of 178.1 nm diameter.

Separately, an aqueous coating solution was prepared by dissolving, in45 g of water, 20 g of a resin mixture consisting of a polyacrylic acidresin and a poly(N-vinylpyrrolidone) resin in a weight proportion of55:45. The resin mixture had been subjected to the test of solubilitybehavior as described before to find that the dissolving time of theresin mixture was one second.

The above prepared patterned resist layer was coated with the aqueouscoating solution followed by a heat treatment at 120° C. for 60 secondsto effect thermal shrinkage. Thereafter, the coating layer was washedwith water at 23° C. to find that removal of the coating layer wascomplete by washing for 60 seconds. The hole pattern diameter could bereduced to 157.4 nm and the cross sectional profile of the patternedresist layer was excellently orthogonal.

COMPARATIVE EXAMPLE 2

A coating solution for comparative test was prepared by dissolving 5 gof a polyvinyl alcohol resin in 95 g of water. Separately, the polyvinylalcohol resin was subjected to the solubility test to find that removalof the coating layer was still incomplete even after 120 seconds of thewashing time.

A test of coated thermal flow process was undertaken in the same manneras in Example 5 excepting the use of the above prepared polyvinylalcohol solution as the coating solution to find that no acceptablepatterned resist layer could be obtained due to remaining residue of thecoating layer on the substrate.

COMPARATIVE EXAMPLE 3

The testing procedure was substantially the same as in Example 5 exceptthat no coating layer was formed on the patterned resist layer. Theresult of the test was that substantially no reduction of the patterndimension could be obtained.

EXAMPLE 6

A semiconductor silicon wafer was spin-coated with a positive-workingphotoresist composition (TDUR-P036PM, supra) and subjected to apre-baking treatment at 80° C. for 90 seconds to form a photoresistlayer of 560 nm thickness.

The photoresist layer was pattern-wise exposed to light on alight-exposure machine (Model Canon FPA-3000EX3, supra) followed by apost-exposure baking treatment at 120° C. for 90 seconds and thensubjected to a development treatment with a 2.38% by weight aqueoussolution of tetramethylammonium hydroxide to give a patterned resistlayer having a hole pattern of 178.1 nm diameter.

Separately, a polyacrylic acid resin was subjected to thewater-solubility test by using an aqueous solution of 5.0 g of the resinin 45 g of water to find that the dissolving time was 1 second.

The hole-patterned resist layer was coated with the aqueous solution ofthe polyacrylic acid resin followed by drying to form a dried coatinglayer thereon and then subjected to a heat treatment at 120° C. for 60seconds to effect thermal shrinkage of the patterned resist layerfollowed by washing with water at 23° C. to find that removal of thecoating layer was complete by washing for 1 second and the diameter ofthe hole pattern was reduced to 161.4 nm.

EXAMPLE 7

A semiconductor wafer was spin-coated with the same positive-workingphotoresist composition as used in Example 6 followed by a pre-bakingtreatment at 80° C. for 90 seconds to form a photoresist layer of 560 nmthickness which was subjected to a pattern-wise light-exposure in thesame manner as in Example 6 followed by a post-exposure baking treatmentat 120° C. for 90 seconds and then a development treatment in the samemanner as in Example 6 to give a hole-patterned resist layer having ahole diameter of 178.1 nm.

Separately, a water-soluble poly(N-acryloylmorpholine) resin wassubjected to the water-solubility test by using a 10% by weight aqueoussolution of the resin to find that the dissolving time of the resinouslayer was 1 second.

The above prepared hole-patterned resist layer was coated with anaqueous solution of the water-soluble resin tested above and dried toform a coating layer of the resin which was subjected to a heattreatment at 120° C. for 60 seconds to effect thermal shrinkage of thepatterned resist layer followed by removal of the coating layer bywashing with water to find that removal of the coating layer wascomplete by washing for 1 second and the diameter of the hole patternwas reduced to 166.9 nm.

EXAMPLE 8

A semiconductor silicon wafer was spin-coated with the samepositive-working photoresist composition as used in Example 6 followedby a pre-baking treatment at 80° C. for 90 seconds to form a photoresistlayer of 560 nm thickness which was pattern-wise exposed to lightfollowed by a post-exposure baking treatment and a development treatmentin the same manner as in Example 6 to form a patterned resist layerhaving a hole pattern of 180.3 nm diameter.

The thus formed patterned resist layer was coated with a 10% by weightaqueous coating solution of a water-soluble resin which was a copolymerof acrylic acid and N-vinylpyrrolidone in a copolymerization ratio of55:45 by weight followed by a heat treatment at 120° C. for 60 secondsto effect thermal shrinkage of the patterned resist layer and thenremoval of the coating layer by washing with water to find that removalof the coating layer was complete by washing for 60 seconds and thediameter of the hole pattern, of which the cross sectional profile wasexcellently orthogonal, was reduced to 157.4 nm.

EXAMPLE 9

A semiconductor silicon wafer was spin-coated with a photoresistcomposition (TDMR-AF2000, a product by Tokyo Ohka Kogyo Co.) followed bya pre-baking treatment at 90° C. for 90 seconds to form a photoresistlayer of 1.3 μm thickness, which was pattern-wise exposed to light onthe same exposure machine as used in Example 2 followed by apost-exposure baking treatment at 110° C. for 90 seconds and developmentin the same manner as in Example 2 to give a trench-patterned resistlayer of 411.1 nm dimension.

The thus obtained trench-patterned resist layer was subjected to thecoated thermal flow process in just the same manner as in Example 8 sothat the dimension of the trench pattern of the resist layer, which hadan excellently orthogonal cross sectional profile, was reduced to 219.5nm.

COMPARATIVE EXAMPLE 4

The experimental procedure was substantially the same as in Example 9excepting for the omission of coating on the patterned resist layer witha coating solution of a water-soluble resin. The result was that noreduction could be obtained in the width of the trench-patterned resistlayer.

COMPARATIVE EXAMPLE 5

The experimental procedure was just the same as in Example 9 except thatthe aqueous coating solution of the water-soluble resin was replacedwith a 5% by weight aqueous solution of a polyvinyl alcohol. The resultwas that, after removal of the coating layer by washing with water,trace of the coating layer could be clearly detected by visualinspection.

EXAMPLE 10

The experimental procedure was just the same as in Example 8 except thatthe coating layer of a water-soluble resin on the patterned resist layerwas formed by using a 10% by weight aqueous solution of a copolymericresin of acrylic acid and N-acryloylmorpholine in a copolymerizationratio of 1:1 by weight. The result was that removal of the coating layerby washing with water was complete by washing for 1 second and the holediameter of the hole-patterned resist layer, which had an excellentcross sectional profile, was reduced to 159.7 nm.

EXAMPLE 11

The procedure for the formation of a hole-patterned resist layer on asemiconductor silicon wafer was just the same as in Example 1 exceptthat the hole pattern obtained had a diameter of 180.3 nm. The procedureof the coated thermal flow process was also just the same as in Example1 except that the aqueous coating solution of a water-soluble resin wasa 10% by weight aqueous solution of a copolymeric resin ofN-vinylpyrrolidone and N-vinylimidazolidinone in a copolymerizationratio of 1:3 by weight. The result was that removal of the coating layerwas complete by washing with water for 60 seconds and the diameter ofthe hole pattern of the resist layer, which had an excellentlyorthogonal cross sectional profile, was reduced to 170.1 nm.

EXAMPLE 12

The experimental procedure was just the same as in Example 2 except thatthe aqueous coating solution of a water-soluble resin in Example 2 wasreplaced with the coating solution used in Example 10. The result wasthat the trench width of the trench-patterned resist layer, which had anexcellently orthogonal cross sectional profile, was reduced to 345.3 nm.

1. A method for reducing dimensions of a resist pattern on a substratewhich comprises the steps of: (a) coating a patterned resist layer on asubstrate surface with an aqueous coating solution comprising awater-soluble resin and a water-soluble amine compound to form a coatinglayer; (b) drying the coating layer of the aqueous coating solution; (c)subjecting the dried coating layer to a heat treatment to effect thermalshrinkage of the coating layer and reduction of the distance betweenresist patterns; and (d) removing the coating layer by washing withwater.
 2. The method as claimed in claim 1 in which the water-solubleresin is selected from the group consisting of alkyleneglycol-basedpolymers, cellulose-based polymers, vinyl polymers, acrylic polymers,urea-based polymers, epoxy-based polymers, melamine-based polymers andpolyamide-based polymers.
 3. The method as claimed in claim 1 in whichthe aqueous coating solution contains from 3 to 50% by weight of thewater-soluble resin.
 4. The method as claimed in claim 1 in which thewater-soluble amine compound is selected from the amine compounds havinga pKa value in the range from 7.5 to 13 at 25° C.
 5. The method asclaimed in claim 1 in which the amount of the water-soluble aminecompound contained in the aqueous coating solution is in the range from0.1 to 30% by weight based on the amount of the water-soluble resin. 6.The method as claimed in claim 1 in which the temperature of the heattreatment in step (c) is lower than the softening temperature of thepatterned resist layer.
 7. The method as claimed in claim 4 in which thewater-soluble amine compound is monoethanolamine or triethanolamine. 8.A method for reducing dimensions of a resist pattern on a substratesurface which comprises the steps of: (a2) coating a patterned resistlayer with an aqueous coating solution containing a water-soluble resin,which is a copolymer of (meth)acrylic acid and an ethylenicallyunsaturated monomeric compound selected from the group consisting ofN-vinylpyrrolidone, N-vinylimidazolidinone, methyl acrylate, methylmethacrylate, N,N-dimethylacrylamide, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropyl acrylamide, N-methhylacrylamide,diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate andN-acryloylmorpholine; (b2) drying the coating layer to form a driedcoating layer of the water-soluble resin; (c2) subjecting the driedcoating layer to a heat treatment to effect thermal shrinkage of thecoating layer and reduction of dimensions of the resist pattern; and(d2) dissolving away the coating layer by washing with water.
 9. Themethod as claimed in claim 8 in which the water-soluble resin is acopolymer of (meth)acrylic acid and the ethylenically unsaturatedmonomeric compound in a copolymerization ratio in the range from 4:1 to1:1 by moles.
 10. The method as claimed in claim 8 in which the heattreatment in step (c2) is conducted at a temperature lower than thesoftening temperature of the patterned resist layer.
 11. A method forreducing dimensions of a resist pattern on a substrate surface whichcomprises the steps of: (a2) coating the patterned resist layer with anaqueous coating solution containing a water-soluble resin which is ahomopolymer of N-vinylpyrrolidone or a copolymer of N-vinylpyrrolidoneand a comonomer which is N-vinylimidazolidinone, N-acryloylmorpholine ora combination thereof to form a coating layer of the aqueous coatingsolution; (b2) drying the coating layer to form a dried coating layer ofthe water-soluble resin; (c2) subjecting the dried coating layer to aheat treatment to effect thermal shrinkage of the coating layer andreduction of the resist pattern dimension; and (d2) dissolving away thecoating layer by washing with water.
 12. The method as claimed in claim11 in which the water-soluble resin is a copolymer of N-vinylpyrrolidoneand N-vinylimidazolidinone.
 13. The method as claimed in claim 12 inwhich the water-soluble resin is a copolymer of N-vinylpyrrolidone andN-vinylimidazolidinone in a copolymerization ratio in the range from 9:1to 1:9 by moles.
 14. The method as claimed in claim 11 in which thetemperature of the heat treatment in step (c2) is lower than thesoftening temperature of the patterned resist layer.
 15. An aqueouscoating solution used in the coated thermal flow process for reducing aresist pattern dimension of a patterned resist layer on a substratewhich comprises a water-soluble resin and a water-soluble aminecompound.
 16. The aqueous coating solution as claimed in claim 15 inwhich the water-soluble resin is selected from alkyleneglycol-basedpolymers, cellulosic polymers, vinyl polymers, acrylic polymers,urea-based polymers, epoxy polymers, melamine-based polymers andpolyamide polymers.
 17. The aqueous coating solution as claimed in claim15 in which the water-soluble amine compound has a pK value in the rangefrom 7.5 to
 13. 18. The aqueous coating solution as claimed in claim 15in which the water-soluble amine compound is monoethanolamine ortriethanolamine.
 19. The aqueous coating solution as claimed in claim 15in which the amount of the water-soluble amine compound is in the rangefrom 0.1 to 30% by weight based on the amount of the water-solubleresin.
 20. An aqueous coating solution of a water-soluble resin used inthe coated thermal flow process for reducing a resist pattern dimensionof a patterned resist layer on a substrate in which the water-solubleresin is a copolymer of (meth)acrylic acid and an ethylenicallyunsaturated monomeric compound selected from the group consisting ofN-vinylpyrrolidone, N-vinylimidazolidinone, methyl acrylate, methylmethacrylate, N,N-dimethylacrylamide, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropyl acrylamide, N-methhylacrylamide,diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate andN-acryloylmorpholine.
 21. The aqueous coating solution as claimed inclaim 20 in which the water-soluble resin is a copolymer of acrylic acidand N-vinylpyrrolidone.
 22. An aqueous coating solution of awater-soluble resin used in the coated thermal flow process for reducinga resist pattern dimension of a patterned resist layer on a substrate inwhich the water-soluble resin is a copolymer of N-vinylpyrrolidone andN-vinylimidazolidinone.
 23. A method for selection of a water-solubleresin used in the coated thermal flow process for reducing the patterndimension of a patterned resist layer formed on a substrate surfacecomprising the steps of forming a coating layer of a water-soluble resinon a patterned resist layer, subjecting the coating layer to a heattreatment to effect thermal shrinkage of the coating layer and reductionof the pattern dimensions and removing the coating layer by washing withwater, which comprises the steps of: (a3) forming a coating layer of thewater-soluble resin on the surface of an unpatterned but photocuredphotoresist layer on a substrate surface; (b3) subjecting the coatinglayer of the water-soluble resin at 140° C. for 60 seconds; and (c3)dissolving away the coating layer of the water-soluble resin by washingwith water at 23° C. to determine the dissolving time taken for completeremoval of the coating layer.
 24. The method as claimed in claim 23 inwhich the water-soluble resin is selected from the group consisting ofacrylic polymers, vinyl polymers, cellulose-based polymers andalkyleneglycol-based polymers.
 25. The method as claimed in claim 24 inwhich the water-soluble resin is an acrylic polymer or a vinyl polymer.26. The method as claimed in claim 25 in which the water-soluble resinis an acrylic polymer.
 27. The method as claimed in claim 23 in whichthe temperature of the heat treatment in step (b) is lower than thesoftening point of the photocured photoresist layer.